Automotive electrical systems are generally designed to match the generator capacity to the normal operating electrical loads. However, due to the numerous electrical devices that are now used in various types of vehicles, and the likelihood that at least some of these devices will be used when the engine is not operating and the generator is not producing power, the incidence of undercharged batteries has become common. Any vehicle that is not used for a few weeks while the battery remains connected to the electrical system is likely to have undercharged or discharged batteries. This is also true for trucks and recreational vehicles that use auxiliary batteries to power household amenities when the vehicle is stopped. The auxiliary batteries are isolated from the main automotive batteries, so they can be independently discharged. When the vehicle is started, either by slave starting or by using the isolated batteries that were not discharged, the high charge load from the discharged battery, in addition to normal operating electrical loads, may exceed the generator capacity. When this happens, the system voltage is well below normal and there is little chance for the generator to recharge the batteries as well as maintain the regulated voltage.
Low voltages induced by electrical overload can impair operation of electronic devices needed for normal operation of the vehicle. A short circuit in the battery or in its cabling can completely inhibit the generator from producing output. Discharged batteries also have significantly less filtering capacity to reduce the generator ripple voltage that is the result of rectifying the generator's alternating current output. The peak-to-peak ripple voltage when the battery is disconnected may in some cases be equal to the direct current battery voltage. Excessive ripple voltage due to discharged batteries can disrupt various electronic fault detection circuits and give false alarms concerning alternator integrity.
Accordingly, there is a need for a vehicle battery charging and load control system that reduces or eliminates the disruption to the regulated voltage necessary for running the electrical devices connected to a vehicle electrical system that can occur from high charging loads demanded by discharged batteries.